Detection of Flame Propagation During Knocking Combustion by Optical Fiber Diagnostics

This paper presents results on the phenomenon of knocking (detonation) during combustion in a single-cylinder spark ignition engine. The investigation of knocking combustion was made possible by observing in-cylinder flame propagation with a measuring technique that uses optical fibers coupled with photo-multipliers.

The results indicate that knocking combustion appears to occur as a result of autoignition and/or acceleration of the flame front in the squish crevices. At high knock intensities, the flame front velocity can be supersonic.

The occurrence of knock damage does not necessarily correspond with location of knock onset. Rather, knock damage is observed at a location where pressure waves, induced by detonation, are reflected and accompanied by pressure peaks.